1. Field of the Invention
The present invention relates to ternary metal transition metal non-oxide nano-particles, methods for preparing the nano-particles and applications relating, in particular, to the use of said nano-particles in dispersions, electrodes, rechargeable batteries and capacitors.
2. Background of the Invention
Transition metal based non-oxide materials such as transition metal nitrides (“TMN”) are known in the art for their high-melting temperature (e.g., approximately 3000° C.), hardness (e.g., Hv=approximately 1800 to 2100 kg/mm2), electronic conductivity, chemical inertness, abrasion and wear resistance. These characteristics have made them useful for abrasion-resistant applications, optical coatings, low-resistivity contacts and as diffusion barrier layers in the microelectronics industry, as well as catalysts in the petroleum industry. Transition metal materials, such as TMNs, have also been found to exhibit surface-induced electrochemical characteristics rendering them useful as electrodes in capacitors.
Electrodes are key elements in energy storage and conversion devices, including, for example, batteries, fuel cells and capacitors. Technological advances in the electronics industry have created a substantial and on-going need to reduce electrode volume and weight to attain increased electrical and electrochemical energy and power densities. In the case of batteries and fuel cells, electrical and electrochemical energy storage and peak power generally relate to the available surface area of the electrode; thus, increasing the stored energy and peak power without increasing the weight and volume of the electrodes can be accomplished by increasing the surface area of the electrodes. In the case of capacitors, typically two mechanisms are found to be most common. First, there is what is known as the electrochemical double layer capacitors (“EDLC”), where the charge storage is primarily dependent on the surface area of the electrode. Second, there is a type of capacitor which is a pseudo-capacitor, whereby the charge storage is driven more by the Faradaic electrochemical charge transfer related to distinct oxidation and reduction reactions. In recent years, a third type of capacitor response has received much attention due to the ability to generate nano-structured forms of the electrode materials providing a combined influence of surface and electrochemical related charge storage mechanisms. This combined effect has led to these capacitors being referred to by the term “super-capacitors.”
Electrical energy is stored in a capacitor, and super-capacitors are a relatively new type of electrical charge storage condenser as outlined above. Electrochemcial capacitors are useful for providing a rapid supply of a large quantity of electricity over a short period of time. Super-capacitors are characterized by orders of magnitude higher power densities, as compared to batteries; although, the energy densities are significantly lower. Super-capacitors are, thus, emerging as energy storage systems that could potentially change the direction of power electronics since compact electronic components with very large capacitances could be manufactured. Some of the important applications of super-capacitors include high-power devices for energy storage systems, voltage stabilizers, power failure protection and memory back-up for computers, displays and video-recorders. Further, applications comprising a hybrid arrangement with an energy storage capacitor for handling the peak power and a battery for handling the sustained load can also be envisioned.
Preferred materials for use in capacitors include noble metal oxides, such as RuO2 and carbon. However, transition metal materials, such as TMNs, are good electronic conductors and offer the potential to exhibit high gravimetric and volumetric capacitance due to their large molar densities. Furthermore, Ru is expensive and its reserves are limited. As for carbon, although the raw materials are cheap, significant improvements will be needed to increase the volumetric power density using economic approaches. Thus, there is a need for exploring new systems that can display superior capacitance with good cycling stability and voltage response time.